Each week, Digital Spy rounds up the biggest mobile gaming releases with reviews and trailers. This week's games include Sega's shape-shifting kart racer, monsters hungry for oil and a minimalist RPG on the go.

Sonic & All-Stars Racing Transformed

Reviewed on: iPhone 4SPlatforms: iPad, iPhonePrice: £2.99 / $4.99

With Sonic & All-Stars Racing Transformed the team at Sumo Digital brings Sega's kart racing series with the overly-long name to iOS.

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The port manages to pack in most of the tracks and characters from the console edition, though with notable exceptions in the roster like Nights and only three tracks per grand prix cup instead of four.

Acceleration is now automatic, with an on-screen button to drift around turns and the option to steer either by tilt or with a virtual joystick. The tilt controls are recommended since they are actually calibrated quite well, though you need to be careful while piloting aircrafts not to tilt so far forward or back that it flips the screen.

Yes, the twisting tracks will occasionally demand that each racer's car transforms into a plane or a speedboat to offer a new twist on the race, whether it's the speedboat's water physics or navigating over and under obstacles in a plane.

On top of the single-player grand prix and online multiplayer races, Sonic & All-Stars Racing Transformed includes a version of the world tour mode, offering challenges like flying through rings or hitting boost strips.

World tour is where you will unlock most of the characters and grand prix cups, so you'll spend most of your time there and notice it has taken some F2P inspiration from other mobile games.

Each world tour challenge has four stars to collect for completing it on different difficulty settings, but only one of the difficulties will be free to race any time.

Competing for the stars on other difficulty settings will cost you rings for each attempt, while the hardest difficulty in each event will cost you one of those hard-earned stars.

The game is admittedly generous in rewarding you with rings after each event, but the entire format of requiring entry fees for races is a significant change from the more player-friendly version of the game on other platforms.

Sonic & All-Stars Racing Transformed on iOS may suffer compared to versions of the game on other systems, but for kart racers on a smartphone it's one of the best games in town.

The levels offer interesting variety through a mix of underwater and open air puzzles, with puzzles taking into account the ways oil behaves differently in each environment.

Simply completing a level isn't a particularly taxing challenge though, and most players will fly through the game earning one-star rankings in little time at all.

However, to get the full three stars for each level you will need to solve the puzzles without using all of the tools at your disposal. Leaving out one tool earns a second star while leaving out two earns you the full ranking.

Feed Me Oil 2 is a fun and charming puzzle game that won't leave you stuck scratching your head over a solution for hours.

As your knight charges in the desired direction he will automatically engage enemies as he bumps into them, taking damage with each bump but also earning experience and valuable gems when the foe is defeated.

After plowing through a line of enemies you'll reach a tavern, where you can spend those precious gems on upgrading the knight's abilities before marching into the next enemy group.

It's incredibly simple, but also remarkably compelling thanks to clever visual touches that upgrade the knight's appearance along with his abilities.

Before long you'll reach the point where the knight can mow down an entire level of enemies in seconds, lighting on fire as he dashes, and it's hard not to be charmed by it all.

Loot Hero is a short experience, with it possible to reach the dragon in under 10 minutes, but the difficulty increases each playthrough to encourage you to charge through it all again.

You may not want to play through it again immediately, but it's a game definitely worth keeping installed on your smartphone or tablet for when the urge for something quick and fun strikes you.